Linked clone virtual machines (VMs) are two or more virtual machines that share storage. Linked virtual machines support efficient sharing of duplicated data. The shared storage for linked virtual machines is achieved through the use of delta disks. A delta disk is a virtual disk file that resides on top of a base virtual disk backing file. Each time a guest operating system on a virtual machine writes to disk, the data is written to the delta disk associated with that virtual machine. Each time a guest operating system on a virtual machine reads from disk, the virtual machine first targets the disk blocks in the delta disk. If the data is not on the delta disk, the virtual machine looks for the data on the base disk.
Linked clone virtual machines can be created from a snapshotted disk (base disk or delta disk) of a virtual machine. After a linked clone virtual machine is created, the linked clone virtual machine shares the disk chain (base disk and/or delta disk) with one or more other virtual machines, while each virtual machine has its own delta disk.
A linked clone virtual machine can be promoted to a full clone virtual machine by using a virtual machine promotion process. Promoting the linked clone virtual machine can improve the performance of the virtual machine. However, current solutions require the linked clone virtual machine to be powered off while it is promoted to a full clone virtual machine. If a large amount of data needs to be copied, the downtime for the virtual machine can be lengthy.